Add benchmark tests

[kseo]

We need benchmark tests before working on performance optimizations such as CodeChain-io/foundry#45 and CodeChain-io/foundry#46.

[somniumism]

@sgkim126 @kseo Four benchmarks already exist in /benches; bench_read_multiple, bench_read_single, bench_write_multiple and bench_write_single.
Could you explain to me what additional work I need to do?

[sgkim126]

You can add any benchmark tests that can show the performance of #2 and #3 has increased.